JPS6332191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for developing a magnetic latent image, and more particularly to a method for developing a magnetic latent image using a magnetic toner charged with a specific polarity.

Conventionally, as a method for developing magnetic latent images, toner containing ferromagnetic material in resin (so-called magnetic toner) has been used.
A method in which a toner brush is deposited on a toner carrier and lightly contacted with a magnetic latent image carrier (Japanese Patent Publication No. 50-90342), a toner brush is formed on a sleeve containing a permanent magnet, and the brush is attached to a magnetic latent image carrier. A method of rubbing the image carrier (Japanese Unexamined Patent Publication No. 100732/1983) is known. However, when so-called insulating toner, which has a charge of a specific polarity, comes into contact with a latent image carrier, it adheres to areas where there is no magnetic signal due to electrostatic adhesion, resulting in fogging on the white background. Easy to appear. In addition, since such insulating toner has a high aggregation property, when a thick layer is formed to bring the toner into light contact with the magnetic latent image, toner agglomerates are likely to occur, and due to such aggregation, the stability is It is extremely difficult to obtain such a thick layer. On the other hand, in order to prevent the above-mentioned fogging and aggregation, it is possible to slightly reduce the toner electrical resistance to prevent electrostatic adhesion and aggregation, but in this case, if the electrical resistance is low, one-shot development will not be possible. This method is not practical because it is difficult to transfer a toner image onto plain paper by corona discharge.

The present invention overcomes these conventional drawbacks and provides a developing method for obtaining a visible magnetic latent image that is fog-free, clear, and transferable to plain paper.

In the present invention, a toner carrier carrying magnetic toner charged with a specific polarity is brought close to a rotating magnetic latent image carrier, and an electric field formed between the magnetic latent image carrier and the toner carrier is suppressed. Under the action of an electric field with alternating directions, the toner is reciprocated between the magnetic latent image carrier and the toner carrier, causing the toner to adhere to the magnetic latent image carrier, and the toner attached to the magnetic latent image carrier to be magnetized. A first step of returning the latent image from the latent image carrier to the toner carrier, and a second step of reducing the strength of the electric field in the first step to visualize the latent magnetic image in accordance with the magnetic attraction. This is a method for developing a magnetic latent image, which is characterized in that development is carried out using a magnetic latent image.

The present invention does not develop a magnetic latent image only with the magnetism of magnetic toner, but develops it under an electric field with alternating directions of the electric field, which utilizes the charged polarity of magnetic toner.
By reciprocating the magnetic latent image carrier back to the toner carrier using an electric field, the supply of magnetic toner to the magnetic latent image is ensured, and the magnetic latent image is maintained with a balance between magnetic restraint and electric field dependence. It is possible to achieve adhesion of the desired amount of magnetic toner.

Hereinafter, details of embodiments according to the present invention will be described with reference to the drawings.

In FIG. 1a, 1 is a toner carrier, and 2 is a highly insulating magnetic toner. The magnetic toner is uniformly coated onto the toner carrier in a layer thickness of 40μ to 500μ by the method described later in this specification, and the magnetic toner is applied to the toner carrier with a layer thickness of 40μ to 500μ, and the magnetic toner is coated with a layer having a negative polarity, for example, by friction with the surface of the toner carrier. A tribo-electrification series has been set up that charges the battery. 3 is a magnetic latent image holder, and the gap between it and the toner carrier is 100μ to 700μ. Moreover, there is a gap between the toner layer and the surface of the toner layer. Since there is a gap between the surface of the toner layer and the latent image holder, the toner does not come into contact with the area of the latent image holder where the magnetic signal is not applied (hereinafter referred to as the non-image area). Toner does not stick. However, when there is a void like this,
Since the magnetic field generated by the magnetic latent image is a close force, toner is difficult to transfer even to the area to which the magnetic signal is applied (hereinafter referred to as an image area), and sufficient development is not performed.

In FIG. 1b, a back electrode 4 is provided on the magnetic latent image carrier, the toner carrier is made conductive or an electrode is provided, and a direct current bias, for example, a positive voltage is applied between the two electrodes on the latent image carrier side. In this case, a negative voltage was applied to the toner carrier side. In this case, if the negative voltage is made sufficiently large, the toner can be sufficiently transferred from the toner carrier to the image area with the help of the electric field. However, at this time, toner transfer to non-image areas also occurs, resulting in the problem of so-called white background fog.

Here, the principle of magnetic latent image development according to the present invention will be explained as follows.
As shown in the figure. In the figure, the latent image holder 3 is rotating in the direction of the arrow. The toner carrier 1 also rotates, preferably at the same speed and in the same direction as the latent image carrier. These 1 and 3 come close to each other to reach the nearest region A, and gradually move away again (region B),
An alternating voltage is applied between the back electrodes 1 and 4 from the power source 5.
It is applied from

Now, due to this alternating external electric field, the toner carrier 1
Efth is the minimum electric field required for toner transfer to the non-image area of the latent image carrier to occur, and Efth is the minimum electric field required for the toner transferred to the non-image area of the latent image carrier to return to the toner carrier (reverse transfer). Let the minimum electric field be Erth.
In addition, in region A, the maximum generated electric field in the phase of the alternating voltage that acts to transfer the toner from the toner carrier to the magnetic latent image carrier is Emax, and the toner is transferred from the magnetic latent image carrier to the toner carrier. The minimum generated electric field in the phase that acts as -
Let's call it Emin. At this time, Emax>Efth, Emin>Erth...(1) is set so that it is satisfied. Although the relationship at this time is shown in FIG. 3, this alternating waveform is schematic and is not limited to this.

With this setting, in the time interval _t1 , the maximum generated electric field Emax acts to transfer the toner particles from the toner carrier 1 toward the electrostatic image holder 3, so this stage is called the toner transfer stage. .
In addition, in the time interval _t2 , the minimum generated electric field Emin tends to return the toner transferred to the electrostatic image carrier in the time interval _t1 to the toner carrier, so this stage is referred to as a toner reverse transfer stage. It is called.

If 1 is satisfied, in region A, the toner repeats reciprocating motion between the magnetic latent image holder and the toner carrier according to the frequency of the alternating electric field. Therefore, in this area, sufficient toner adheres to the image area and a certain amount of toner adheres to the non-image area.
However, there is no problem because the toner adhering to this non-image area will be removed in the next area B as described later. Rather, in this region A, by making the toner more or less adhere to the non-image area, the adhesion of the toner to the image area is made more complete, and the image density due to the magnetic field is reduced as much as possible. It is essential to deposit faithful magnetic toner. As a result, a visualized image with excellent gradation can be obtained.

When reaching region B, the distance between the toner carrier and the magnetic latent image holder increases, so although the applied voltage remains constant, the alternating electric field strength decreases.

The boundary between areas A and B is the point in the non-image area where toner transfer from the toner carrier to the latent image carrier can no longer occur, and the relationship at this time is Emax=Efth...( 2).

Then, when Emax<Efth Emin>Erth...(3), toner transfer from the toner carrier to the latent image carrier can no longer occur in the non-image area, and reverse transfer from the latent image carrier to the toner carrier A situation arises in which only one thing happens unilaterally. Therefore, all of the toner adhering to the non-image area in this area is reversely transferred to the toner carrier, and white background fog does not occur. On the other hand, in the image area, even if the toner carrier and the latent image carrier can reciprocate in the area closest to them, when they move apart, the toner is restrained by the proximity force of the latent image magnetic field. Therefore, the toner does not return to the toner carrier, and therefore, sufficient development density is ensured.

Then, Emin=Erth...(4) and the above-mentioned toner reverse transfer ends, so
This time is the end point of region B.

The arrows shown in the regions A and B indicate the directions of the toner transfer and countertransference as described above.

It can also be considered separately as follows.

｜Emax−Efth｜＞｜Emin−Efth｜＞0
......In a region that satisfies (5), the amount of toner transferred from the toner carrier to the latent image carrier is larger than the amount of reverse transfer.

When the gap further increases, |Emax−Efth|<|Emin−Efth| ...(6), and the amount of toner reverse transfer becomes larger than the amount of toner transfer.

What is important here is that there is an upper limit to the frequency of the applied alternating electric field. That is, as the frequency was increased, the γ value gradually increased, and the effect of increasing the gradation from high to high faded. The cause of this is
It can be considered as follows. During the development process in which an alternating electric field is applied, when the toner repeatedly undergoes transfer and reverse transfer between the toner carrier surface and the electrostatic image forming surface,
A finite response time is required to reliably reciprocate. In order to reproduce halftone image densities, it is necessary that toner subjected to an electric field of a certain threshold value or more be reliably transferred within a half cycle of the alternating electric field. For this purpose, it is advantageous to have a low frequency of the alternating electric field, and particularly good gradation can be obtained in the low frequency region. As the frequency is increased, the gradation quality decreases, and for this reason it is best to use a frequency of 1KHz or less, but there is no problem in using it for digital recording, and it is possible to use frequencies up to 10KHz.

On the other hand, if the frequency is too low, the reciprocating movement of the toner will not be repeated sufficiently while the latent image forming surface passes through the developing section, and uneven development will likely occur in the image due to alternating voltages. As a result of the above experiment, the frequency is 60Hz.
Up to this point, generally good images were obtained, but below that point, unevenness occurred in the visible images. It has been found that the lower limit of the frequency that does not cause unevenness in such a microscopic image is particularly dependent on the development conditions, particularly the development speed (also referred to as process speed, Vpmm/sec).

In this experiment, the moving speed of the electrostatic image forming surface was 200
mm/sec, the lower frequency limit is 60/200×V _p =0.3×V _p (Hz).

As described above, in order to improve gradation and remove background fog, it is preferable to appropriately set the combination of frequency and electric field strength.

It has been confirmed that any waveform of the applied alternating electric field, such as a sine wave, a rectangular wave, a triangular wave, a sawtooth wave, or an asymmetric wave thereof, is effective. Further, the time interval between the phase of toner transfer and the phase of reverse transfer may be different.

In order to achieve the above development, the toner layer on the toner carrier must be formed thin and uniformly. The present invention also provides a toner supply coating method and means suitable for developing a magnetic latent image by the above-described developing method.

Next, an embodiment of the developing device according to the present invention will be described with reference to the drawings.

Embodiment 1 This will be explained with reference to FIG.

FIG. 4 shows one embodiment of the present invention, in which the toner carrier is a non-magnetic sleeve 6 containing a permanent magnet 7 therein. Reference numeral 8 denotes a magnetic (iron) blade facing one main pole position of the magnet 7, which is held at a gap of 200 μm from the surface of the sleeve 6. Under the action of a magnetic field, the toner is deposited on the sleeve. It forms a thin layer. The toner contains about 25% to 60% of a magnetic material (ferrite, magnetite, etc.) in a resin such as polystyrene or polyester, and further includes a charge control agent and a coloring agent as necessary. Reference numeral 11 denotes a power supply for applying an alternating electric field that performs the above-described function. This alternating electric field consists of an alternating current with a frequency of 600 Hz and an amplitude of 1600 V _pp (peak-to-peak value), with a 100 V direct current superimposed on it. Of course, such asymmetrical alternating current is just one example, and it goes without saying that other alternating waveforms such as rectangular waves, triangular waves, pulsed waves, etc. can also be used.
The toner, which has been regulated to a coating thickness of about 80 microns by the action of the magnetic field, is conveyed to the developing position by the rotation of the sleeve 6 due to the electrostatic adhesion force to the sleeve 6. Near the development position, no magnet is placed inside the sleeve 6 in order to prevent the magnetic latent image from being destroyed by the magnetic force of the magnet. What is noteworthy is that by using the toner supply coating and developing method of the present invention as described above, the area where no magnet is provided (10 in the figure) can be made sufficiently wide. The effectiveness of this is obvious when compared with, for example, ordinary magnetic brush development. That is, in magnetic brush development, since it is necessary to form a brush at the development position, a magnetic field is inevitably required, and there is a high possibility that the magnetic latent image will be destroyed.

Of course, it is possible to provide magnetic poles at the development position to an extent that does not destroy the magnetic latent image. Experiments have shown that better development can be achieved in some cases when there are minute magnetic poles in the developing section, but a magnetic brush of the level that is applied to normal magnetic brush development is not possible.

Embodiment 2 This will be explained with reference to FIG.

In the figure, 1 is a toner carrier, which is a belt made of stainless steel or conductive rubber. 6'
is a rotating sleeve containing a fixed magnet 7'.
Reference numeral 8 denotes a magnetic (iron) blade, which is disposed at a position facing one main pole 7a of the fixed magnet 7' with a gap of 100 to 400 microns from the sleeve.
Under the action of the magnetic field acting between 7a and 7a, the toner 2 is transferred onto the toner carrier at 50 to 50°C as the sleeve rotates.
Uniformly coated to a thickness of 300μ. Toner carrier 12
is made to face the magnetic latent image holder 3 by a roller 13, and development is performed. The reason why the roller 13 is provided separately from the sleeve 6' to form the developing section is to prevent the magnetic latent image 3 from being destroyed by the magnetic field generated by the sleeve 6'.
Reference numeral 11 denotes a power source that applies the above-mentioned alternating current voltage to the roller 13. The toner 2 is insulative and is charged by friction with the surface of the toner carrier. The toner once applied by the blade 8 is conveyed to the developing section by the electrostatic adhesion force with the toner carrier 12, and good development is performed as described above.

FIG. 6 shows a specific example of the overall configuration of an image forming apparatus to which the embodiment shown in FIG. 4 is applied. Reference numeral 3 denotes a drum-shaped magnetic latent image holder formed by the magnetic recording head 14, which rotates in the direction of the arrow. Of course, the holding body may have another shape such as a belt.

15 is a device for developing such a magnetic latent image;
The details are as described above, but to give an example of a specific embodiment, first, the magnetic toner is made of 50% styrene acrylic resin and magnetite.
48%, negative charge control agent 2% (both weight%)
It has a composition of , and is negatively charged. This magnetic toner is regulated by a magnetic blade 8 placed at a gap of 250 μm from the surface of the toner carrier. Gauss), the toner layer that has formed into a curtain shape is doctored by a magnetic field, so it is approximately 100 μm.
It is possible to form a toner layer with a thickness of . The toner layer thus thinly applied is conveyed to the development position as the toner carrier rotates, and is subjected to development under the above-mentioned alternating electric field. The alternating bias power supply 11 at this time has a +100 V direct current superimposed on an alternating current with a frequency of 600 Hz and an amplitude of 1600 _Vpp . The process speed at this time was 200 mm/sec. In this way, as mentioned above, a fog-free and rich gradation image can be obtained.
It is sent to a transfer position by a corona discharger 16. The latent image holding body after transfer is cleaned by a known cleaning means 17.
The residual toner is removed by the eraser head 18, and the latent image carrier is finally made reusable by the erasing head 18.

The present invention is not limited to the embodiments described above, but includes all embodiments included within the spirit of the invention.

A moving toner carrier carrying magnetic toner charged with a specific polarity is brought close to a rotating magnetic latent image carrier, so that the direction of the electric field formed between the magnetic latent image carrier and the toner carrier is alternating. Under the action of an electric field, the toner is moved back and forth between the magnetic latent image carrier and the toner carrier, causing the toner to adhere to the magnetic latent image carrier, and the toner attached to the magnetic latent image carrier to retain the magnetic latent image. The first one returns from the body to the toner carrier.
, and a second step of reducing the electric field strength of the first step and visualizing the latent magnetic image according to the magnetic attraction force. This method has the effect of completely solving the above problems and making it possible to obtain a developed image with excellent gradation without background fog.

[Brief explanation of the drawing]

Figures 1a and 1b are diagrams explaining the principle of the conventional developing method;
FIG. 2 is a diagram explaining the principle of an example of the developing method of the present invention;
Figure 3 is a characteristic diagram of an example of the alternating electric field waveform.
5 and 5 are cross-sectional views showing embodiments of the present invention,
FIG. 6 is an explanatory diagram of an example of the overall configuration of an image forming apparatus incorporating the aspect of FIG. 5. 1... Toner carrier, 3... Latent image carrier, 2...
...magnetic toner, 11...alternating voltage source.

Claims (1)

[Claims] 1. A toner carrier that carries magnetic toner charged with a specific polarity and moves is brought close to a rotating magnetic latent image carrier, and a toner carrier is formed between the magnetic latent image carrier and the toner carrier. The toner is caused to reciprocate between the magnetic latent image carrier and the toner carrier under the action of an electric field whose direction is alternating, causing the toner to adhere to the magnetic latent image carrier and to adhere to the magnetic latent image carrier. a first step of returning the toner from the magnetic latent image carrier to the toner carrier; and a second step of reducing the strength of the electric field in the first step to visualize the magnetic latent image in accordance with the magnetic attraction. A method for developing a magnetic latent image, characterized in that development is carried out by performing the following steps. 2 The electric field in the first step is defined as the moving speed of the magnetic latent image holder, where Vp (mm/sec) is the frequency of the alternating electric field, and (Hz) is the frequency of the alternating electric field.
The method for developing a magnetic latent image according to claim 1, wherein V _p is greater than 0.3 times and less than 10,000. 3. The magnetic toner carrier contains a fixed magnetic field generating means for conveying the magnetic toner inside the developing sleeve, and the fixed magnetic field generating means is located at the closest portion of the magnetic latent image carrier and the toner carrier. The magnetic latent image developing method according to claim 1, wherein the fixed magnetic field generating means does not have a magnetic field generating magnetic pole.